The present invention relates to drawing of elongated stock to be withdrawn from a suitable store (drum, spool, vessel, etc.) and under utilization of straightening equipment, drawing die equipment and equipment for pulling the stock through the straightening and drawing equipment.
Drawing of elongated stock, particularly metal tubing usually requires one end of the tubing to be passed through the die to permit gripping of that end on the other side of the die by means of particular clamps on a take up, coiling and capstan drum. As this drum rotates, the stock as pulled through the drawing die for reduction of the cross-sectional dimensions of that tubing.
The stock used here is comprised, for example, of tubing which has been extruded from a billet and is subsequently passed through a rolling mill to stretch roll or the like the tubing for reducing its diameter. These steps preceding drawing involve inherently tubes of short length. The stock drawn is accordingly not too long. On the other hand, drawing speeds used today are quite high so that the idle periods between drawing passes have about the same duration as the respective periods of drawing. Thus, the drawing proper has a duty cycle of only about 50%. Production speed is, therefore, limited by the duration of the period between two drawing passes. The preparation for the next pass can be carried out to some extent only during the current pass, such as introducing a mandrel into the next tubular blank and to form a pointed end to be inserted into and threaded through the die. Threading the tube end into the die, and fastening it to the pulling drum has to wait until the current pass has been completed.
Additionally, it has to be considered that the tubular stock to be drawn may arrive in coiled configuration, so that the length of tubing has to pass through straightening rolls before being pulled through a drawing die. Threading the end portion through the tubing is another preparatory step to be carried out before this particular length can be stretch formed.